Many factors such as politics and oil prices have contributed to an increase in deep offshore oil exploration of depths up to 3000 m. New technology such as floating production storage and offloading (FPSO) platforms and subsea production wells has enabled efficient deepwater offshore exploration. This technology necessitates the use of flexible risers, umbilicals, control lines, and other flexible pipes. Flexible pipes offer mobility and flexibility from the standpoint of designing systems. Flexible pipes are suitable for carrying process chemicals back and forth from the bottom of the ocean and subsea wells to floating platforms at sea level. Their length may range from about 1500 to about 3000 m long. Flexible pipes are also suitable for transporting other fluids than crude oil, including hydrocarbon liquids and gases, such as natural gas. In fact, flexible pipes can be useful for transporting virtually any fluid in any environment, including when the fluid to be transported and/or the environment where to transport it, is chemically aggressive.
Flexibility is a distinctive property of a flexible pipe. A typical 8″ internal diameter flexible pipe should desirably bend to a radius of about 2 m or even less. This flexibility is important notably for floating production systems, and also for flowlines laid on difficult seabed conditions; flexibility makes it further possible to spool the pipe on a reel or in a carousel for efficient and quick transportation and installation. Yet, flexible pipes must also be strong enough to survive stresses imparted by waves, currents, and tides as well as severe pressures and sharp temperature fluctuations.
Flexible pipes are generally made up of several layers arranged in a modular construction, i.e. at least some of the pipe layers are independent from each other; desirably, all the pipe layers are independent from each other. Such independent, un-bonded layers are to a certain extent able to move relative to one another so as to allow the pipe to bend. They have also the additional advantage that they can be made fit-for-purpose and independently adjusted to best meet a field development requirement.
Flexible pipes include generally corrosion-resistant steel wires as main usual components. The steel wires are generally helically wound, so as to give the structure its high pressure resistance and excellent bending characteristics, thus providing flexibility and superior dynamic behavior. The wound steel wires are desirably insulated from each other by intermediate polymer abrasion layers.
Precisely, polymer layers are other usual main components of flexible pipes. In addition to their possible highly beneficial use as antiwear sheaths, polymer layers are also useful as leakproof barriers. The outermost layer of a flexible pipe may advantageously be made of a polymer leakproof barrier, which prevents the external environment medium (such as sea water, when drilling offshore) from penetrating inside the flexible pipe structure. At the opposite, the innermost layer of a flexible pipe may also advantageously be made of a polymer leakproof barrier, which prevents the transported fluid (such as crude oil or natural gas, e.g. when drilling offshore), from moving towards the more outer layer(s) of the flexible pipes.
Prior art flexible pipes the design of which are well adapted for offshore exploration are described in the standardized documents published by the American Petroleum Institute (API), and especially documents API 17J and API RP 17B. This type of pipe comprises successive layers, independent of one another, including, on the one hand, helical windings of profiled wires and/or tapes and, on the other hand, at least one sheath made of a polymeric material. Whereas the function of the metal layers is to take up the mechanical forces, both internal and external, the function of the polymeric sheaths is to provide internal or external sealing. The various layers are to a certain extent able to move relative to one another so as to allow the pipe to bend. Various structures exist for such pipes, however they all generally have a multilayer assembly called a pressure vault that is intended to take up the radial forces and a multilayer assembly intended to take up the axial forces. The pressure vault located toward the interior of the pipe generally consists of a short-pitch helical winding of a profiled wire, while the layers intended to take up the axial forces, located toward the outside of the pipe, generally consist of a pair of cross plies of armor wires wound helically with a long pitch. In addition, to prevent at least two of these armor plies coming directly into contact with one another, which would result in their premature wear, a relatively thin intermediate layer of plastic is interposed. Flexible pipes equipped with antiwear layers are described in U.S. Pat. No. 5,730,188 (to Wellstream, Inc.) and WO 2006/120320 (to Technip France), the whole content of both patent titles being herein incorporated by reference. The reader may refer to FIG. 1 of US' 188, wherein polymer layers 14 and 16 are used as antiwear sheaths of a flexible pipe; the same pipe includes also a polymer layer 12, which acts as overlying fluid barrier. The reader may also refer to FIG. 1 of Technip's PCT application: a flexible pipe, with a design pretty close to that of Wellstream's one, includes anti-wear plastic layers 22 and 24, as well as a pressure sheath 8 and a covering layer 10, the pressure sheath 8 and the covering layer 10 being also possibly made of polymer.
Whatever their location and function in the flexible pipe multilayer assembly, the polymer layers need to comply with multiple harsh requirements, including high compressive strength, high temperature resistance, hydrolytic stability at high temperatures, toughness and ductility for winding, environmental stress cracking resistance and abrasion resistance.
When a polymer layer is used as the innermost layer of a flexible pipe, it is subject to chemical attack by the transported fluid, especially in the hot underground environment in which down-hole pipes convey oil from deeply buried deposits to the earth surface. Should the transported fluid be oil, the sulfur, sulfur dioxide and carbon dioxide present in the oil typically make it acidic causing corrosion of the interior surface of the pipe. The innermost layer of a flexible pipe may also be abraded by materials insoluble in the oil, including materials which are soluble in the oil at high temperatures of the oil deposit but become insoluble as the oil cools during the rise through the pipe to the earth surface; among such resultant insoluble materials, it can be cited asphaltenes, paraffin waxes and “scale” which generally includes calcite and/or barite. Further, to avoid plugging by these materials, it may be necessary to clean out the internal surface of the pipe by mechanical scrapping (pigging), chemical or hot oiling treatment, which by its aggressive nature, requires the innermost layer to exhibit a high chemical and abrasion resistance.
When a polymer layer is used as the outermost layer of a flexible pipe, this one may also be corroded by the external environment medium. Typically, when drilling offshore, it may be corroded by sea water. Such water may contain carbonic or hydrochloric acid, and occasionally oil and gas may contain small amounts of corrosive gases such as carbon dioxide and hydrogen sulfide. When either of these gases are dissolved in water, acid is created that may attack the surface of the pipe, causing its possible failure. Further, typical oil well operations include running flexible pipes down hole with appropriate tools; the repeated spooling may cause fatigue and wear damage that can suddenly cause the outermost layer to fracture and fail.
Intermediate polymer layers, in particular antiwear polymer layers, tend to deteriorate particularly rapidly when the flexible pipes of which they are made up are subjected to severe stresses, such as those encountered when extracting certain subsea oil deposits, located at great depth, and where the hydrocarbon is at a high temperature of around 130° C.; under such conditions, these ones layers may endure temperatures of around 110° C. and contact pressures (compressive stresses) of about 300 to 400 bar. In addition to being subjected to severe stresses, intermediate polymer layers, in particular antiwear layers, have to withstand abrasion and friction at an extremely high degree of intensity, typically much higher than that endorsed by the other layers. Further, intermediate polymer layers further be subject to chemical attack resulting from local contacts with chemical agents of the same nature as those with which the innermost and/or the outermost layers are in direct contact. Finally, one or more faces of the intermediate polymer layers, in particular of antiwear layers, may be locally or completely covered by a lubricant, such as some kind of grease, to reduce somehow the wear intensity caused by the metal armor plies, and make it easier their relative motion with regard to the same.
Various polymers have already been proposed as the main component of a polymer layer of a flexible pipe, including polyolefins, polyurethanes, polyethers, poly(vinylidene fluoride)s, polyamides, poly(amide imide)s, polyimides, poly(ether imides), polyphenylene sulfides, wholly aromatic polyesters, poly(aryl ether sulfone)s and poly(aryl ether ketone)s. The reader may notably refer to US 2005/0121094, US 2006/0127622 (to Du Pont), U.S. Pat. No. 5,601,893 (to Elf Atochem), GB 1 443 225 and GB 2 330 394 (to the Institut Francais du Petrole), EP 1 186 819 (to ABB Research Ltd.), EP 1 741 549 (to UBE), WO 99/67561 (to ABB Offshore Technology) and WO 05/103139 (to Exxon Mobil Chemical), the whole content of all these patent titles being herein incorporated by reference.
However, there is a still a strong need for a flexible pipe comprising one or more polymer layer(s) made up of a polymer material, including but not limited to intermediate antiwear layers, wherein the said polymer material would exhibit an improved overall balance of properties, including a high compressive strength, a high temperature resistance, a high hydrolytic stability at high temperatures, a high toughness and ductility for winding, a high environmental stress rupture resistance and a high abrasion resistance, all this at a lower cost than that of a high performance semi-crystalline polymer like PEEK, and which would further be well-adapted to processing by extrusion in long tape form. In particular, the said polymer layer(s) should exhibit an environmental stress rupture resistance and an abrasion resistance close to those exhibited by polymer layers made up of high performance semi-crystalline polymers like PEEK, but at a lower cost and with a good long tape extrudability. Desirably, the said polymer layer(s) should exhibit at least substantially the same environmental stress rupture resistance and abrasion resistance as those exhibited by polymer layers made up of PEEK, but at a more attractive cost and with a good long tape extrudability.
The Invention
This need, and still other ones, are met by a flexible pipe (fP) suitable for transporting hydrocarbons, said flexible pipe comprising at least one polymer layer (L) composed of a polymer composition (C) comprising:                at least one poly(aryl ether ketone) (P1), and        at least one per(halo)fluoropolymer (P2), and        optionally at least one polyarylene (P3), and        optionally at least one poly(aryl ether sulfone) (P4),wherein, if polyarylene (P3) is present, the total weight of the poly(aryl ether ketone) (P1), based on the total weight of the polymer composition (C) is above 50%, and wherein, if poly(aryl ether sulfone) (P4) is present, the total weight of the poly(aryl ether sulfone) (P4) over the total weight of the poly(aryl ether ketone) (P1) ratio is below 1.        
According to another aspect, the invention provides a method for producing the flexible pipe (fP) as above defined, wherein the polymer composition (C) is extruded, thereby simplifying its processing and in particular allowing long thin sheets to be formed.